Experts from Australia to Colorado sensed the earthquake immediately as it shook the Indian ocean floor. But because of bureaucratic inertia, diplomatic protocol and primitive communications, news of the impending catastrophe never reached the beaches and coastal communities lying in its path.

Bayu Pranata was sipping tea shortly after starting his 7 a.m. shift at the Meteorology and Geophysics Agency in West Sumatra, Indonesia, about 500 miles south of the quake's epicenter, when he was disturbed by a "tak, tak,...